ITs open source in the same way OSX and iOS are open source (although more open, i will admit) the core is open, but a very large proportion of the key services are closed and difficult to replace.
I can give you a link to the AOSP repository.
If iOS and OS X are open source in the same way than Android, then you can give us a link to the repositories, isn't?
Can I fork OS X and make another operating system based on it?